Paraquat persistence

Paraquat is relatively immobile in soil. Paraquat resists hydrolysis, photodegradation in water, and microbial degradation under both aerobic and anaerobic conditions. Dissipation is primarily by adsorption to organic material and clay particles. As paraquat persists in clay soils, it may be found in surface water from erosion. Since it binds so strongly to clay particles, paraquat is not generally a ground-water concern. 

Paraquat is used to control aquatic weeds. It also passes into aquatic environments through rain, where it is rapidly accumulated by aquatic organisms, especially fish (Gabryelak and Klekot 1985). Paraquat applied to control aquatic weeds is accumulated by aquatic macrophytes and algae, and it is adsorbed to sediments and suspended materials. Initial applications of 1 to 5 mg/L in the water column are usually not detectable under field conditions after 8 to 27 days (Summers 1980). The half-time persistence of paraquat in water column at normal doses for weed control (i.e., 0.5 to 1.0 mg/L) was 36 h less than 0.01 mg/L was detectable in 2 weeks (Calderbank 1975). In solution, paraquat was subject to photodecomposition and microbial metabolism, degrading to methylamine... 

Paraquat tends to rapidly localize in selected tissues of injected mice, including melanin, alveolar type cells of the lung, choroid plexus, muscle, proximal tubules of the kidney, liver, gallbladder, and intestinal contents (Waddell and Marlowe 1980). Half-time persistence of paraquat in rat tissues ranged from 20 to 30 min in plasma to about 5 days in muscle (Sharp et al. 1972). 

The degradation rate of paraquat in certain soils can be slow, and the compound can persist for years — reportedly in a form that is biologically unavailable. But data are missing or incomplete on flux rates of paraquat from soil into food webs and on interaction dynamics of paraquat with other herbicides frequently applied at the same time. It seems prudent at this time to keep under close surveillance the residues of paraquat in soils in situations where repeated applications have been made over long periods of time (Summers 1980). 

Fryer, J.D., R.J. Hance, and J.W. Ludwig. 1975. Long-term persistence of paraquat in a sandy loam soil. Weed Res. 15 189-194. 

Moyer, J.R. and C.W. Lindwall. 1985. Persistence and availability of paraquat in a Lethbridge clay loam soil. Can. Jour. Soil Sci. 65 523-529. 

Uses Paraquat is a colorless, odorless, white or pale yellow crystalline solid that is hygroscopic. Paraquat is a quaternary nitrogen herbicide that is widely used for broadleaf weed control. It is a quick-acting, nonselective compound that destroys green plant tissue on contact and by translocation within the plant. It has been employed for killing marijuana in the United States and Mexico. It also is used as a crop desiccant and defoliant, as well as an aquatic herbicide. Paraquat is highly persistent in the soil environment, with a reported field half-life of greater than 1,000 days.5-7,17... 

Understandably, there are examples of oxygen-tolerant cell lines which have much higher levels of constitutive antioxidant enzymes than normal [249]. The ability of other cells to protect themselves by means of antioxidant enzymes is limited by their biosynthetic response to oxidative stress. In vitro exposure to paraquat induces an increase in SOD and catalase activities in human and hamster fibroblasts [250,251]. In cultured HeLa cells, a chronic exposure to paraquat induces a simultaneous increase in Mn- and Cu/Zn-SOD activities in surviving cells [252], Interestingly, such cells have apparently acquired resistance to paraquat, and their higher level of SOD activities persists for many months following the exposure to paraquat. In Chinese hamster fibroblasts, a chronic exposure to H2O2 results in a 5-40-fold increase in catalase activity [253], which... 

The police were alerted and Susan Barber and her former lover (she had by now acquired a new one) were arrested, nine months after her husband had died. She confessed that she had found the weedkiller Grammoxone in the garden shed and had added some to the steak and kidney pie she prepared for her husband. She claimed that she had only wanted to make him ill, and repeated the poisoning twice when there seemed to be no effect. She had not known that paraquat takes some time to work its unpleasant effects. Susan Barber was convicted of murder on 1 November 1982. An astute and persistent pathologist, together with sensitive and specific chemical analysis, had been her eventual undoing. ... 

Paraquat. Paraquat is a widely used herbicide in cotton and potato culture, on orchard floors, and in landscape maintenance. There have been persistent reports of paraquat poisoning, mostly from ingestion both intentional and accidental, but also from dermal contact. There have also been reports linking paraquat to chronic intoxication, particularly in pulmonary disease from inhaling paraquat aerosols. In addition to food residue analysis in support of tolerance, worker exposure samples and ambient environmental samples are also of great interest. 

The availability of reliable measurements or estimates of water solubility, octanol-water partition coefficient, bioconcentration factor, rate constants and the like allows one to make qualitative judgements or, through the use of mathematical simulation models such as EPA s EXAMS (19), quantitative calculations of environmental distribution and persistence. In the qualitative use, Swann and coworkers (20) classified chemical mobility in soil based upon reversed-phase HPLC retention data which in turn is related to S. The approximate water solubility equivalents in this first-estimate classification, with chemical examples, are in Table II. This classification holds for chemicals whose primary adsorption in soil is to organic matter, and excludes those chemicals (such as paraquat) which bind ionically to the soil mineral fraction. A recent tabulation of pesticides found in groundwater had 11 entries, 8 of which represented compounds with water solubilities in excess of 200 ppm with the remaining three falling in the range of 3.5 to 52 ppm (21). 

Other studies (64) done in the greenhouse showed that paraquat applied to a loamy sand at rates of 50, 100, and 200 Ib/acre was readily absorbed in toxic amounts by blueberry plants. Bioassays with cucumber seedlings showed that the herbicide persisted in the soil long after the blueberry plants had been removed. 

Finally, three examples will demonstrate the structure-activity relationship approach based on comparison of chemical structures. A pyridinium type of ionic liquid is presented in contrast to Paraquat (4), a herbicide which is considered to exhibit substantial toxicological and eco-toxicological risk (due to high acute toxicity and high persistence) and has therefore been banned in many countries. 

Resistance was not initially expected to evolve to paraquat, as this herbicide has no biological persistence it is only a contact herbicide, and is immediately bound to soil colloids. Farmer persistence made up for this resistant weed populations evolved where paraquat was applied 6-10 times annually in a variety of weeds. It was clearly shown that PSI was totally suppressed in isolated thylakoids [cf. 11] in paraquat resistant Conyza, yet extreme membrane damage appeared only in the paraquat treated, intact chloroplasts of the sensitive biotype [37]. Photosynthesis in intact leaves was immediately inhibited in both biotypes, but the resistant biotype recovered in a few hours [37]. 

Akpinar-EIci M, Travis WD, lynch DA, Kreiss K (2004) Bronchiolitis obliterans syndrome in popcorn production plant workers. Eur Respir J 24 298-302 Banauch GI, Alleyne D, Sanchez R, Olender K, Cohen HW, Weiden M et al (2003) Persistent hyperreactivity and reactive airways dysfunction in World Trade Center firefighters. Am J Respir Crit Care Med 168 54-62 Bismuth CH, Hall AH (1995) Paraquat poisoning. Mechanisms, prevention, treatment. Marcel Dekker, New York Basel Hong Kong... 

---